This is a great place to start when looking to see if your garden visitor is friend or foe.
Ants
There are several species of ants in north America; most often they are beneficial, helping to pollinate plants, cleaning up the garden, acting as farmers themselves, or providing food for wildlife. Ants are garden pests only in select cases, so take time to be sure they are causing damage before acting.
HOW TO IDENTIFY: Most common are wingless ants of various sizes and colors. Most ants nest in colonies, in the ground. Ants are known to protect and tend to aphids, and other honeydew-producing pests so they often occur together. Japanese pavement ants chew plants at the soil surface causing them to wilt.
PEST PREVENTION: For potted plants you are bringing indoors, submerge the pot in water with organic insecticidal soap for to kill a potential colony. Avoid planting crops like citrus or calendula that are attractive to scale, aphids, or other honeydew-producing insects, or monitor them closely.
PEST CONTROL: Try to trace ants back to the colony and pour boiling water on the colony. Use organic bait stations like those made with boric acid; ants bring the bait back to the colony causing a colony-wide impact.
CROPS COMMONLY AFFECTED: Specific ant species may be pests to various garden plants, especially in the seedling stage.
Aphids
Common garden pests, aphids feed by sucking plant sap, sometimes spreading plant viruses in the process. Aphids can reproduce quickly but are fairly easy to control and aren't usually detrimentally harmful to plants. Aphids excrete a sticky substance often referred to as "honeydew," which is a food source for ants and a host for sooty mold.
HOW TO IDENTIFY: Aphids are tiny (1/32″–1/16″), slow-moving, pear-shaped, soft-bodied insects that range in color from light yellow to green to black, generally blending in with the plant material they are feeding on, and they may or may not have wings. Their feeding causes distorted leaves, buds, and flowers, and leaves a sticky residue on plants, and stippling (small spots) or yellowing where feeding has occurred. It is not uncommon for aphids to be present in large numbers. If "honeydew" or sooty mold is present, but aphids are not, the aphids may be on an overhanging plant or tree.
PEST PREVENTION: Cover susceptible crops when sowing or upon transplanting with row cover to exclude aphids. Reflective mulches also repel aphids. You can plant flowers that attract natural predators like predatory wasps or ladybug (also called ladybird beetle) larvae, or aphid-repelling plants, such as basil, garlic, chives, and rosemary.
PEST CONTROL: Knock aphids off plants with a strong stream of water--they are slow and weak and have difficulty returning to the plant. Insecticidal soap or horticultural oil sprays can be helpful. These sprays will impact only the insects that are coated with the spray so be thorough and check back frequently. Neem can deter aphids and if they eat it, it also works to control the population.
COMMON CROPS AFFECTED: Some aphids are specialized, feeding on specific crops, but as a group they feed on a wide variety of plants.
Cabbage Worms/Loopers
Cabbage worms/cabbage loopers are caterpillars of various moths and butterflies that feed on and plants.
HOW TO IDENTIFY: Usually the first sign is holes in the leaves of brassica crops and possibly frass (droppings). The caterpillars, commonly known as inchworms, are either green with long white stripes, or green with black lateral stripes and are nearly camouflaged. They are up to 2″ in length and are often on the underside of leaves or tunneled into to heads of cabbage. The adult cabbage worm butterfly is brown with white spots and active in the daytime. Cabbage looper moths are nocturnal, dark and light brown, and mottled.
PEST PREVENTION: Cover brassica crops with row cover upon sowing or transplanting to exclude this pest. Scout for eggs on the underside of brassica crop leaves.
PEST CONTROL: Pick the caterpillars off by hand and drop them into a bucket of soapy water to kill them. Apply Bacillus thuringiensis (Bt) or organic spinosad-based products; they take a few days to kill the caterpillars and need to be reapplied regularly (carefully follow instructions on the packaging). A long-time home control is sprinkling the plants with rye flour or cornmeal in morning dew, with the idea that after the caterpillars eat it, it explodes their digestive system.
CROPS COMMONLY AFFECTED: Brassica crops like Brussels sprouts, broccoli, kale, cauliflower, cabbage, mustards, and so on.
Colorado Potato Beetles
Colorado potato beetles occur in most of the US, despite the name. This pesticide-resistant insect can do some major damage, but like many pests, it is also easy to detect and reduce if caught early.
HOW TO IDENTIFY: Adult beetles are slow moving, about 3/8″ long, oval, yellow-orange with black stripes running from thorax to rear and black spots on their head. Young or larval Colorado potato beetles are reddish-brown with two rows of black spots on their sides and a lateral black stripe on the thorax. Eggs are bright yellow, long ovals laid in clusters of 20–60 on the underside of leaves.
PEST PREVENTION: Row cover can be helpful to exclude potato beetles. Rotate plants in the Solanaceae family, like tomatoes and peppers, out of the area they were grown for at least 3 years.
PEST CONTROL: Straw mulch creates a habitat for predators of young beetles and makes travel difficult for the large, clumsy, adult beetles.
CROPS COMMONLY AFFECTED: Potatoes, tomatoes and mostly other crops in the Solanaceae family.
Corn Earworm
Corn earworm also called tomato fruitworm or cotton bollworm, is a destructive agricultural pest.
HOW TO IDENTIFY: Adult moths are tan, about 1¼″ long and usually nocturnal. They lay yellow, round eggs on corn silks and leaf hairs. Eggs turn green and then gray over time. Larvae are about 1/16″-2″ long caterpillars with a golden-brown head and usually a broad, dark, lateral stripe behind the head. The body color varies from yellow to pink to green, brown, or black but there are usually dark longitudinal stripes present.
PEST PREVENTION: Early detection is key to preventing damage. Inspect plants daily, and corn ears once the silks appear. Extension Services often keep a record of reports of pests like the corn earworm and can be a good resource for taking note of when the pest is in your area.
PEST CONTROL: Plant flowers that attract beneficial insects that eat corn earworm eggs and larvae, such as lacewings, ladybugs, pirate bugs, big-eyed bugs, and soft-winged flower beetles. Inspect your developing corn ears for signs of infestation and remove the pest with tweezers, securing husks again with string or a clothespin. You could also apply five drops of organic insecticide (like neem, spinosad, or Bt that has been mixed with mineral oil) per ear to the silk at the husk opening just as the tips of silks begin to wilt and brown. This will kill any larvae that entered the ear and prevent more from entering.
COMMON CROPS AFFECTED: Sweet corn, green beans, ripe tomatoes, peppers, and a wide range of other plants.
Cucumber Beetles
Cucumber beetles (Striped and Spotted) feed on all parts of plants and fruit possibly spreading bacterial diseases and viruses like bacterial wilt, squash mosaic virus, and powdery mildew. There are several species in North America.
HOW TO IDENTIFY: Cucumber beetles resemble elongated ladybugs but are yellow with black dots or yellow with black stripes and about 1/4″ long. Their worm-like larvae are white with brown heads.
PEST PREVENTION: Apply row cover at sowing or transplanting, until plants begin to flower, to exclude the cucumber beetle. Kaolin clay products create a layer of clay on the leaves and stem of the plant that makes feeding on the plants difficult for the beetles. In long-season areas, delaying planting can help to avoid the worst damage and population build-up which occurs in spring. Remove all damaged plants after fall harvest. Rotate crops so cucurbit crops are not grown in the same area for 3 years. Plant a trap crop of 'Blue Hubbard' squash which is preferred by the beetle to lure them away from other crops.
PEST CONTROL: Apply straw mulch which creates a barrier to the roots where beetles lay their eggs, and also creates a habitat for wolf spiders, which eat cucumber beetles. Planting broccoli, nasturtium, or radish with squash has also been shown to reduce damage from cucumber beetles. Use yellow sticky traps available at your local garden center; hand pick or knock beetles into soapy water; use insecticidal sprays like neem.
COMMON CROPS AFFECTED: Striped cucumber beetles are specialists on cucurbits (such as cucumbers, squash, pumpkin, watermelons), while spotted cucumber beetles feed on other plants in addition to cucurbits.
Cutworms
Cutworms, caterpillars of a number of species of moths, feed on stems and roots of seedlings, severing the plants at ground level.
HOW TO IDENTIFY: Different species can be gray, pink, green, or black, spotted or striped, and as long as two inches. They curl into a "C" shape when disturbed and are often mistaken for grubs (beetle larvae). During the day, they rest just below the soil surface.
PEST PREVENTION: Since peak damage tends to occur in the spring, setting out transplants later in the season could avoid damage. Protect transplants with 3″ collars made of paper, cardboard (toilet paper or paper towel roll cores) or other material surrounding the stem and pushed into the soil 1″. Bacillus thuringiensis or spinosad mixed with a bit of molasses, alfalfa meal, or bran to create bait can be placed on the soil in beds prior to planting (or even after, if necessary). Weed control, fall clean-up, and fall and spring soil cultivation help to reduce cutworm populations.
PEST CONTROL: Scout for this pest at dusk or night when you are most likely to encounter them feeding. Pick them off the plants and destroy.
COMMON CROPS AFFECTED: A wide variety of crops in their seedling stage.
Deer
HOW TO IDENTIFY: If it looks like large bites were taken out of your plants, deer may be the culprit.
PEST PREVENTION: Keep deer out of your garden by using tall fences (over 8′) around your garden or smaller fencing over raised bed or rows. Deer tend to be more likely to jump a fence if they can see what is on the other side, so an opaque fence is a good bet and it can likely be shorter than a see-through fence. Electric fences also work and there are solar options so an outlet nearby is not necessary. Choose plants that deer tend to avoid that have strong smells or textured, leathery, dense, prickly, or fuzzy foliage. There are a lot of deer deterrents, like sprays that do work, but they must be used often (follow manufacturer's instructions).
CROPS COMMONLY AFFECTED: Lots of crops and ornamental plants.
Flea Beetles
Flea beetles chew holes in leaves creating a lace-like appearance, and their larvae feed on roots, especially in spring when they are most destructive.
HOW TO IDENTIFY: At only 1/16″ long, many species are black to tan, but can be other colors, solid or spotted, depending on the species. These tiny, hopping beetles spring away quickly (like fleas) when disturbed.
PEST PREVENTION: In the spring, cut off the food supply to emerging flea beetles by delaying planting by a couple of weeks if possible. Protect young plants with row covers from the time of sowing or transplant; plant trap crops such as nasturtiums, eggplant, or mustard to draw them away from your other plants and then treat or destroy the trap crop to reduce the populations. Grow Brassicas in late summer/fall instead of spring.
PEST CONTROL: Spray with garlic or hot pepper solution and apply frequently. Do fall cleanup/tilling to help reduce their numbers.
COMMON CROPS AFFECTED: A number of crops, but mainly eggplant, tomatoes and Brassicas (alyssum, mustard, broccoli, cauliflower, kale, cabbage, radishes, etc.).
Fungus Gnat
Fungus gnat is usually an indoor pest that hangs around potted plants or an indoor growing area. The larvae feed on plant roots but rarely cause much damage in a home environment. The adults do not harm plants or people, but they are generally a nuisance and do continue the cycle by laying eggs on the soil/medium surface.
HOW TO IDENTIFY: Fungus gnats may be mistaken for fruit flies, small (1/16″–1/8″ long) and dark, but they have longer, clear wings, hang out on growing medium, and are clumsy and slow at flying. The larva is not usually visible but it has a shiny black head and a clear to cream body.
PEST PREVENTION: Fugus gnats need very moist soil for eggs and larvae, so keeping soil or medium on the drier side or letting it dry out between waterings can be helpful. Check any new plants you bring home carefully and keep them separate from other plants for 2 weeks to be sure there are no soil gnats present before exposing other indoor plants.
PEST CONTROL: Yellow sticky traps that can be found at your local garden center are a good start to trap and kill fungus gnats, however, they may not completely knock them out. Bacillus thuringiensis israelensis (Bti) is and effective control.
CROPS COMMONLY AFFECTED: Indiscriminate, since the larvae feeds on diverse organic matter in the soil or growing medium.
Root Knot Nematodes
Root knot nematodes are microscopic roundworms that feed on plant roots, secreting chemicals that cause "knots" or galls(swellings) on the roots. They tend to occur in sandy soils in warmer climates.
HOW TO IDENTIFY: Plants may appear yellow, stunted, or wilt during the day, and have fewer, smaller fruits. Look for galls on the roots of an infected plant. Galls can be confused with beneficial nitrogen-fixing nodules on legumes, so when growing legumes, you may want to compare a questionable plant with a healthy one.
PEST PREVENTION: Choose cultivars that are resistant to root knot nematodes. You should also rotate crops, and transplant only healthy plants.
PEST CONTROL: Remove and destroy infected plants and their surrounding soil. Avoid spreading infected soil through transplanting or tilling, and be mindful to clean tools as to avoid infecting soil in a different area. Weeds are often a host to nematodes, so continue to weed frequently. Grow a cover crop of French marigolds, which attract nematodes and also exude chemicals that reduce their population; dispose of marigold plants (including roots) at the end of the season to remove some of the population In hot summer regions, soil solarization will help to reduce nematodes (but also beneficial organisms) as will letting the area dry out during this time period. Rotating in nematode-suppressing plants like broccoli, cauliflower, rye, or millet can help reduce the population, especially if grown in the affected area for 2 years. Some studies suggest neem, extract-based soil amendments, and soil drenches can be effective in protecting plants from infestation.
COMMON CROPS AFFECTED: A wide range of crops.
Slugs
Slugs are most abundant and damaging during wet years and in high rainfall regions. They feed primarily on soft, tender plant tissue, making large holes in foliage, stems and bulbs, and sometimes completely destroying seedlings. Slugs are typically most active at night or on cloudy days.
HOW TO IDENTIFY: Slugs look a lot like snails without shells. Most types are grey to dark brown, but they can be striped or spotted, and some species are yellow. When they travel, they often leave a shiny, silvery-white trail.
PEST PREVENTION: Slugs will typically avoid copper, so you can use 2″ copper flashing, somewhat buried, as edging for garden beds. Protect seedlings by spreading wide bands of egg shells, coffee grounds, or diatomaceous earth around plants (add frequently and again after rain).
PEST CONTROL: Trap slugs under pots, boards, or melon rinds; collect and destroy every morning. Make traps by burying a container like a bean can with the lip flush to the soil surface; fill with beer or other fermenting liquids and slugs will make their way into it and be trapped in the liquid. Pick by hand and destroy. Use commercially available organic slug bait.
COMMON CROPS AFFECTED: Almost any soft, leafy crops, fruits, and especially lettuce, brassicas, and beans.
Squash Bugs
Both adults and young squash bugs feed on leaves and stems causing black spots that turn crisp. They also cause damage to fruit.
HOW TO IDENTIFY: Squash bugs' shiny bronze-colored eggs are usually found on the underside of the leaves, in a group of about 10–20, in evenly spaced patterns. Nymphs are pale green when young, becoming darker as they mature. Adults are about 5/8″ long, brownish black, fast crawling, flat-backed bugs.
PEST PREVENTION: Sow bug-resistant squash cultivars. Protect young plants with floating row covers (remove covers once flowers form to allow pollination, or hand-pollinate flowers.) Attract parasitic flies with pollen and nectar plants.
PEST CONTROL: Adults are very difficult to kill because they are fast and not susceptible to pesticides, so squishing eggs is the most efficient way to get rid of the bugs. Eggs hatch in about a week, making regular scouting and squishing necessary. Handpick all stages of squash bugs from the plant base and undersides of leaves and squish or put in a bucket of soapy water. Place boards on the ground around squash plants, and destroy adults found underneath every morning by scraping them into a pail of soapy water. Neem (an extract of the Indian Azadirachta indica tree) has an odor that deters gray or brown adult squash bugs, and if they eat it, it disrupts their ability to reproduce, but doesn't kill them. Neem washes off with rains and becomes ineffective more quickly in warm weather; apply in the early morning or evening, after rain, and regularly for it to be most effective. Insecticidal soap and horticultural oil are effective with contact to young nymphs and will need to be reapplied as more appear. Kaolin clay products create a physical barrier to eating and egg laying. Kaolin clay also washes off with rain and will need to be reapplied. Also, sowing crop successions monthly using row cover allows you to trap bugs and destroy infested plants regularly. Squash bugs overwinter on garden debris and mulch so be sure to clean up the garden at the end of the season.
COMMON CROPS AFFECTED: All cucurbit crops, especially squash.
Squash Vine Borers
Squash vine borer moths hatch out of their cocoons that have overwintered in the soil.
HOW TO IDENTIFY: Adults are about ½″ long, black with a red-orange abdomen and black dots. Their top wings are metallic green-black. The larvae are white or cream colored with brown heads, and just under 1" long. The first sign of squash borers is usually eggs laid on the stem near the soil line; next you will see a pin-head sized hole, and what appears to be sawdust near the hole the borer made entering the stem; then part or all of the plant wilts.
PEST PREVENTION: Deter moths by covering the base of the stems near the ground with soil, mulch, foil, or fabric material. Choose resistant varieties. Spray with organic Bacillus thuringiensis aizawai (Bta) or spinosad as soon as moth are seen, as an effective pre-emptive measure. Fill a yellow container with water (vine borer adults are attracted to yellow); the adults will fly to the container and be trapped when they fall into the water.
PEST CONTROL: You can inject the affected stem with Bt to kill the larvae or use a sanitized knife to cut above the entry hole, remove the larvae, and bury the damaged stem in hopes it will create new roots and recover. Otherwise, pull and destroy infected plants. Because the caterpillars overwinter and rise again in the same fields, remove and destroy (do not compost) infected plants to prevent ongoing borer infestations. If your season is long enough, succession-sow crops in early July after the adult borers have finished laying eggs around the first crop.
COMMON CROPS AFFECTED: Squash, pumpkins and, to a lesser degree, cucumbers and melons.